The present invention relates to calibrators for a magnetic azimuth detector, in particular, to apparatus for calibrating a magnetic azimuth detector in an aircraft.
Known compass calibrators inject two precision currents into a magnetic azimuth detector (also referred to as a flux gate or a flux valve) to simulate rotation of the magnetic field of the earth while the aircraft is physically aligned to magnetic north. Prior to injection of these precision currents, the magnitudes of these currents are determined when the magnetic azimuth detector is outside and away from the magnetic disturbances of the aircraft. The magnetic azimuth detector is aligned to magnetic north and optical alignment equipment (e.g. telescope with reticule) is mounted to the magnetic azimuth detector and aimed at a distant monument, structure or geographic feature. Thereafter the magnetic azimuth detector is mounted in the craft using optical realignment equipment and precision currents are injected to simulate rotation.
Other approaches to calibrating a magnetic azimuth detector involve physically revolving the craft while the magnetic azimuth detector is mounted therein, to then characterize its reading as a function of aircraft heading. Such physical rotation requires precisely known physical monuments to precisely align the aircraft. A compass rose has been laid out at many airports for this purpose but utilization, of course, requires flying the aircraft to that facility at a significant cost in time, fuel, labor etc. Alternatively, the aircraft can be flown through a known circular course and the compass reading for the various positions of the aircraft recorded. This approach also requires significant flight time.
In a self-calibrating compass system, the magnetic azimuth detector is corrected by a directional gyro or stable inertial platform. While this approach provides reasonably good accuracy, the initial heading of the aircraft must be precisely known.
Accordingly, there is a need for an apparatus to calibrate a magnetic detector without the need to physically fly or rotate the aircraft. It is desirable that this calibration technique be performed without the need for elaborate and expensive optical alignment equipment and be operable at night and under inclement weather conditions.